Troposheric ducting is one of the most interesting and fun
things about scanning. Durring a duct it is possible to hear stations
on your scanner in the VHF and UHF band from about 50 to 900 mhz that
includes picking up stations hundreds of miles away from your local police
to fm radio to tv.
How does this all work and how can you enjoy it?
The key word hear is "ducting" in your house you use
ducts to shuffle warm and cool air around the house.
Natural atmospheric ducts form that can shuffle VHF and UHF
radio waves well beyond line of sight range. Tropospheric
ducting occurs mostly in the warm weather months of the summer and
sometimes in the presence of large storm systems. This is not to be
confused with skip
these signals are not bouncing of the ionosphere but rather traveling
in ducts several hundred feet above the ground. What causes ducting? Have you ever seen a mirage on the road that looks like water, thats
actualy the sky you are seeing. Light waves that normaly travel in a straight line bounce of the
super heated windless pavement and are reflected back to your eyes.
The same concept durring a duct- but backwards. Typicaly straight line
VHF, UHF signals begin to travel up and away, but are bent back by a sharp boundry layer
of warm, moist air overlying cool dryer air below and above. In the city it's what traps the
smog in and gives us one of those unbearable days get on the radio on that day it will be amazing.
This enhanced signal propogation opens up a whole new
world of scanning such as one of my favorites FM/TV DXing. One way to find out
if a duct is opening up is to monitor tv channels that are not used in your area
for example if your local tv channels are 2 and 6 try to see if 4 or 9 is comming in.
Another way is to monitor those noaa weather frequecies that come on the weather band on your scanner.
If you normaly recieve 162.475 try if you can get 162.550 or 162.400. I have recieved
Noaa weather radio stations over 400 miles away on a regular basis in the summer.
For more info on TV/FM dxing visit my TV/FM dxing page
